1.
INTRODUCTION –
PCB Rev 2
This 50W QCX Power Amplifier has the following features:
Up to 50W power output with 20V supply, falling to around 25W at 13.8V supply
Standard 50-ohm input and output
Fast clean solid-state Tx/Rx switching provides full break-in operation (QSK)
Can be built for one of 80, 40, 30m or 20m bands with the supplied components (or other
bands with suitable choice of Low Pass Filter components)
Uses two low-cost IRF510 transistors as the power amplifier in push-pull configuration
Recommended amplifier operation in Class C
On-board 7-element Low Pass Filter for harmonic attenuation
Two black anodized heatsinks sized 130 x 28mm with 25mm fins typically limit the
temperature rise to < 20C over ambient in normal CW operation
Through-hole plated PCB, all through-hole components (no Surface Mount Devices)
All connectors board-mounted: two BNC, one 2.1mm barrel power connector, one 3.5mm
jack connector for keying
PCB size 130mm x 59.5mm (2.744 x 1.338 inches)
Standard inexpensive components throughout (easy to replace)
Optional black anodized aluminium enclosure
We hope you enjoy building and operating this kit! Please read this assembly manual carefully,
and follow the instructions step by step in the recommended order.
Note that this amplifier is NOT designed for Linear operation; linear operation would
require a higher bias current setting on the PA transistors and would result in higher heat
dissipation; it may be worthwhile experimenting with this but you will be in experimental
territory.
This amplifier is intended for single-band operation and may be built for 80, 40, 30 or 20m using
the supplied components. The band-specifying section of the circuit is the Low Pass Filter (LPF).
You may build it for other bands by suitable choice of low pass filter components; the LPF
component values should be the same as in the QCX kit
, or the QRP Labs
. T50 sized toroids must be used, and NP0/C0G type capacitors
with at least 100V rating, sufficient to handle the 50W output power.
A suitable power supply is required, for full power 50W operation it will need to be capable of
providing at 20V at a current of around 5A.
2.
GENERAL ASSEMBLY GUIDELINES
Assembly of this kit is quite straightforward. But there are quite a lot of components. So please
keep them methodically in trays or some convenient storage boxes. Be careful not to misplace
any. The usual kit-building recommendations apply: work in a well-lit area, with peace and quiet to
concentrate.
Some of the semiconductors in the kit are sensitive to static discharge.
Therefore,
observe Electrostatic discharge (ESD) precautions
.
And
FOLLOW THE INSTRUCTIONS!!
Don’t try to be a hero and do it
without instructions!
A jeweler's loupe is really useful for inspecting small components and
soldered joints. You’ll need a fine-tipped soldering iron too. It is good
to get into the habit of inspecting every joint with the magnifying glass
or jeweler's loupe (like this one I use), right after soldering. This way
50W QCX PA kit assembly
1.00q
4
